test: Bump OPA to 1.12.3

Author: NickLarsenNZ

tests/test-definition.yaml

@@ -19,7 +19,7 @@ dimensions:
       # - x.x.x,oci.stackable.tech/sandbox/airflow:x.x.x-stackable0.0.0-dev
   - name: opa-latest
     values:
-      - 1.12.2
+      - 1.12.3
   - name: ldap-authentication
     values:
       - no-tls